Heat-sensitive copying-paper



Fel 2, 1954 N. w. TAYLOR ETAL v 2,668,126

HEAT-SENSITIVE COPYING-PAPER Filed Jan. 5, 1950 wwf/Wy MMMY@ Patented Feb. 2, 1954 HEAT-SENSITIVE COPYING-PAPER" Nelson W, Taylor, White Bear Lake', and -Bryce IL'.v Clark,"-St. Paul, Minn., assignors tofMinnesotaL4 Mining & Manufacturing Company, ISt.a fP-aul, Minn., a corporation of Delaware Application January-5, 1950," Serial No;`136;944':

' 4Claimsl (Cl. ILL-36') Thisf" invention'- is concerned-' with duplicator sheet "material orcopying-paperv useful l in f pre-l contemplated-are `of fpa'rticular utilityin making copies of?!graphicsubject-rnatter such as printingdiawings; diagrams; pictures, etc. by methodsfto be descrbedf Such'` methods involve the irradiation of-l the graphic subject-matter with interi'se:` radiant energy of i proper f Wave-length, the resultantformatiori of an elevated-temperatrepattern'correspondinglto -vthe graphic matterfirrafdiated; and-the utilizationA of such elevated-temperature pattern inl'directly producing a corresponding visible pattern in the copyingpaper.

Depending. on-the desired appearance of the finished copy,. we may employ a transparent, dyed-pigmented, or-` othertype of base-sheet material-forourl novel copying-paper, provided r the sheet has a low degree ofv heat-conductivity; For most purposes, we prefer to use writing-paper having on--one'surface a thin but opaque 'colored coating. To this .sheet we apply a-thin.uniform= layer or a-mixtu-re ofy fusible-waxyJ particles and infusiblel siliceous-particles in a solution of a film-forming-infusible transparent binder. The.

volatile vehicleis thenremoved by evaporation ata-temperature below the melting-point of the waxy particles'.- Thewdried coating is opaque, and the coated sheet is quite resistant to surface marring.

Inmaking a copy of graphic subject-matter, e; g. of a typewritten page,Y we-place the copyingpaper, vprepared as described above, in close and heat-conductive--contact with the unprinted surface ofthepage. typewritten surface to-intense radiant energy. O n removing, and examining the 1 copying-paper,

it' isfiound'tovcontainal visible copy ofthe printed message, a'ppfearir'igV in the color ofthe base sheet against a background of unchangedlwax-silica coating.

Suitable radiant' energy for such copying methods may' be obtained from electricallyheated` incandescent' filaments, electric arcs,

focused sunlight; etc. and is largely. within the The mostv infra-red or near infra-red range.V convenient source" is the electric lanent, par- We then brieflyv expose the 2; Y tially enclosed b'y a suitable reflector, and-"the copying-paper isi-therefore: designed to .printl at temperatures;- abov'e ncrmalf roomandi storage temperatufr'es,l which `Yit is Vpossibleto reach safely-- by irradiation of thef'graphic material f from such f' source ofradiantenergy;

Cellophane or othertransparentf-iil-n materialL may-constitutef the exi-blefvsupport for they fusible layer; in which case tneifcopyfwill: appear as transparent? areas:A inv an; opaque.. background.'r` Paper orother fibrous '-sheet material, vas-'Well as# theJnon-brous llr'ns; mayfb'e used eitherf in `the natural color or after beingcolored'with an ap` propriate dye, this colored backing thenbeing.: visible through i the transparent* spaces.'obtainedv in the opaque coatingfd-uringthe copying process: For'the most-intense copy,` however,I we prefer -to coat'theiiexible'backing: with :an opaque?. colcred'contrast-layer aslpreviouslyfdisclosed A1 compositionisuitablei fore this purpose.v may cony sist of -lampblack'dispersed in' albind'erI of cellua f lose acetate@lacquer.'v Various coloredfpigmentsf. e-.l g. -nigrosine; ultramarineytoluidinef toner,` etc., mayreplace th'efflanfip-blackf, vand-'othercellulosi'c y lacquers;r4 spirit: varnish'es,-lelastomer"v solutions,4 or

the?. fusible layer Vmayv adhere," .andi must provide.

adequate :visual .contrast when-present as 'an ex'- trem'elyi thin .lm;

The waxy particles must remain. in particulate form -atln'orrnal Vr'oom and!! storage-temperatures, butmust meltlandfuse together;atttemperaturesf obtainable th`e copying; process, to form a continuous'v transparent waxy" layer. which4 re mains transparent on'c'ooling toroom tempera-Y ture.A Naturall ester-type waxes" (such as: carnaubaf wax), vhydrocarbon waxes, andA other, wax-y materials or mixtures thereof, f whichi are suitably# transparent andi meltl withinA the appr'oxinlate range ofi60e150 G., or preferably 'l0-120 C., may be. employed.-r Water-insoluble salts* ofhigher fattyl acids Shave -been found tol givev excellent results Oner suc-h -waxy materialis cadmium stearata:prepared.v by theV reactionY of..a solublecadmium saltwitl the water-soluble' sodium saltlof commercialtriple-pressed stearic acid. Other examples. arelead: myristate and lead palmitate.

The infusible siliceous particles are substantially. transparenty and have a refractive index approximately 'the same as that ofthe waxy/"maf terial. Fibrous or' acicula'r'infusible transparent" particles such as asbestine may be used. Cuslfie'cl2 However, when an attempt is made to produce.

copies of printed pages or the like by methods herein described, it is found that the fused porA tions of the coating adhere to the printedA4 page =or other contiguous surface and subsequently are pulled away from the copying-sheet.,Further-1 more, these two-component coatings are susceptible to removal by rubbingbrushing, or flaking. A small anic-unt of a nlm-forming binder is therefore dissolved in the volatileyehiclawand serves to hold the particles together and to the base sheet without/'seriously reducing the opacity of the particulate coating. Cellulose acetate and ethyl cellulose are examples of film-forming binder materials soluble in volatile liquid vehicles which are non-solvents for the preferred waxy materials. These binders, like the siliceous particles, are infusible at temperatures required to fuse the wax, and have approximately the same refractive index as the wax.

The opacity of the coating is due partially to the waxy particles, and partially to the infusible siliceous particles. The individual small particles are held in place by partial contact with each other and with the binder, but are largely separated so that light impinging on the layer of particles is diffused and scattered. With the surface coating in this condition, the colored conv trast layer beneath it cannot be Seen.

As previously noted, graphic subject-matter may be directly copied by placing the copyingpaper against the reverse side of the printed sheet and strongly irradiating the printed surface. In explanation of this effect, it is believed that the radiant energy directed against the printed page or the like is largely reflected from the unprinted surface but is absorbed and converted to heat at the printed areas. The resulting elevated temperature pattern at the irradiated surface is sufficient to produce a corresponding elevated-temperature pattern within the fusible layer and to cause fusion of said layer at the heated areas. The fusible material, which as a solid is immobile, in the fused or liquid form immediately wets and flows around the adjacent infusible siliceous particles, yforrning a matrix in which the particles are embedded on cooling. The infusible binder remains attached to the siliceous particles and distributed throughout the waxy matrix, and in addition a portion appears to remain as a fllm at the outer surface of the matrix. Since all three components have substantially the same refractive index, the resulting compacted composite layer is transparent and does not cause objectionable optical distortion. The underlying layer of the copying-paper is thus exposed to view through this transparentized portion of the opaque coating, and a facsimile of the original graphic subject-matter is obtained.

Placing the opaque particulate surface of the copying-paper against the reverse side of the printed sheet results in the production of a direct copy of the original, and is ordinarily preferred. The copying-paper may, however, be otherwise positioned if desired. rihus, placing the uncoated surface of the copying-paper against the reverse side of the printed sheet makes possible the 4 formation of a reversed copy of the original graphic subject-matter.

In the figure, which is a diagrammatic enlarged vertical cross-section, not necessarily to scale, of one embodiment of our novel heat-sensitive copying-paper, the sheet is seen to consist of a iiexible contrasting support I2 coated with an opaque layer I3 consisting of a mixture of particles I4 of fusible waxy material and particles iof siliceous infusible particles (in this case represented as small glass spheres), held together and to the supporting base by a small amount of infusible binder I6. A portion of the binder forms a semi-continuous surface film I1.

Various modifications of the exemplary copying-paper here described and illustrated will be apparent to those skilled in the art, particularly in View of the discussion herewith presented. Thus, the support I2 may be coated on either surface with a color layer, or may be dyed or pigmented; or if transparent, the copy may be held against an illuminated transparent surface or against an opaque contrasting surface, in order to provide desired visibility of the copy. However, the support l2 should be low in heat conductivity, hence metal foil and the like is excluded. Although not ordinarily desirable, an ad- `itional light surface nlm of binder material may be added to fortify the film I1.

The presence of the infusible particles I5 is found to provide a number of advantages. Substitution of the quite inexpensive crushed glass or analogous particles for the relatively expensive wax particles eifects a desirable saving in costs. The infusible particles provide a hard outer surface for the heat-sensitive layer. When the heatsensitive surface is pressed against a sheet of paper in making a copy, the infusible particles assist in preventing the melted wax from iiowing to and into the paper.

Example Paper was first provided with a black contrast layer of lamp-black and cellulose acetate, as previously described, and over the contrast layer was applied a coating of a heat-sensitive composition comprising lead palmitate, ethyl cellulose, and small glass beads.

Lead palmitate is a water-insoluble metal salt' of a long-chain fatty acid, and is a waxy material melting at approximately 99-101o C. It was dispersed in acetone, in the form of fine particles within the approximate size range of 1,(2-25 microns, by prolonged ball milling. The concentration was 26%. An ethyl cellulose soluble in acetone was used, and it was added as a preformed solution in acetone, at a concentration of 10%. No. 19 glass beads, of about 3 mils diameter, were employed. The two solutions and Lthe dry beads were mixed in various proportions, and the mixtures coated on the prepared backing and dried at room temperature. The coating was found to fuse and become transparent when briefly heated to about 954.95 C. The sheets were then tested as heat-sensitive copying-papersv according to the method described herein for making direct copies.

With l0 parts by weight of beads and 100 parts of the wax, best results were obtained with three parts of ethyl cellulose binder. Less than about one part of the binder was insufficient to prevent dusting and rub-off of the heat-sensitive layer. More than about six parts of ethyl cellulose reduced the opacity of the coating, and copiesmade with these sheets were undesirably low in contrast.

With 50 parts of beads and 100 parts of wax, somewhat the same results were obtained over the range of 1-6 parts of binder except -that there was a slight reduction in detail o-f the copies. Rub-off occurred with less binder. At nine parts of binder, iiaking was noted; apparently the lm strength of the coating exceeded the adhesion between backing and coating.

Still higher ratios of beads to wax, up to equal parts of each, gave good results with the lower proportions of binder, but at six parts binder to 100 each of wax and beads, aking again occurred. Above about 100 parts of beads, flaking and reduced detail made the coatings ineffective for most copying purposes.

The foregoing tests were on sheet material coated on a knife coater at an orifice of six mils, which was found to be the minimum coating weight at which full opacity and maximum contrast was obtained. At three mils, the sheet appeared grey in color, due to the contrast layer showing through the partially translucent coating. Furthermore, the composition was difficult to apply at that thickness due to the size of the glass beads. At nine mils, the opacity was no better than at six mils, and the detail of the copy was obscured.

Larger size particles also reduced the amount of detail obtainable, and tended to make the copy fuzzy and dilcult to read. No. 14 beads, with a diameter of about four mils, represent an approximate maximum size. Much smaller particles may be used, but the increased surface area of fine powders per unit of weight requires that the amount of such materials be limited. Mixtures of various sizes and types of infusible transparent particles sometimes provide additional advantages.

The product of our invention, in its preferred form, is thus seen to consist of a visibly contrasting thin fiexible poorly heat-conductive support member coated with a heat-sensitive opaque layer of a mixture of insoluble siliceous particles and fusible waxy particles held in place with an infusible film-forming binder, the components being suitably selected and proportioned in accordance with the requirements and disclosures herein set forth. The product is stable to light, being capable of prolonged exposure to actinic radiation without change, and is not activated at normal room or storage temperatures. At higher temperatures, and particularly within the range of about 60-150" C., or preferably within the more restricted range of about 70-120 C., which temperatures may be readily and safely attained byintense irradiation of a contiguous printed page with infra-red rays, the heated opaque layer is irreversibly converted to a transparent condition,

permitting the visibly contrasting support member to be seen.

This application is a continuation-in-part of of our copending application Serial No. 747,341,

' filed May l0, 1947, now abandoned.

What we claim is as follows:

1. A light-stable, heat-sensitive copying-paper adapted to provide clear and sharp copies of typewritten messages by methods herein described,

- comprising a thin flexible visibly contrasting support member having low heat conductivity and a thin opaque heat-transparentizable surface coating comprising a mixture of: (a) one hundred parts by weight of particles of transparent waxy material fusible at about 60150 C.; (b) about 10-100 parts by weight of transparent infusible siliceous particles less than about four mils in diameter; and (c) sufficient ltransparent flexible organic film-forming bindenwithin the range of about one to about six parts by weight, to provide good resistance to dusting and rub-off of the coating Without causing flaking thereof; the wax, siliceous particles, and binder each having substantially the same refractive index, and said binder being infusible at the fusion temperature of said wax.

2. Product of claim 1 in which the waxy material is a water-insoluble metal salt of a longchain fatty acid and is fusible at about 70-120 C.

3. Product of claim 2 in which the waxy material is lead palmitate.

4. A light-stable, heat-sensitive copying-paper adapted 4to provide clear and sharp copies of typewritten messages by methods herein described, comprising a thin flexible visibly contrasting support member having low heat conductivity and a thin opaque heat-transparentizable surface coating comprising a mixture of (a) one hundred parts by weight of particles of transparent waxy material fusible at about 60-150 C.; (b) about 10-100 parts by Weight of transparent glass beads of about three mils diameter; and (c) sufficient transparent flexible film-forming cellulosic binder, infusible at the fusion temperature of the waxy material, and in an amount within the range of about one to about six parts by weight, to provide good resistance to dusting and rub-olf of the coating without causing flaking thereof; the wax, glass beads, yand binder each having substantially the same refractive index.

NELSON W. TAYLOR. BRYCE L. CLARK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,783,422 Mayer Dec. 2, 1930 2,269,038 Perry Jan. 6, 1942 2,313,810 Dalton Mar. 16, 1943 

1. A LIGHT-STABLE, HEAT-SENSITIVE COPYING-PAPER ADAPTED TO PROVIDE CLEAR AND SHARP COPIES OF TYPEWRITTEN MESSAGES BY METHODS HEREIN DESCRIBED, COMPRISING A THIN FLEXIBLE VISIBLY CONTRASTING SUPPORT MEMBER HAVING LOW HEAT CONDUCTIVITY AND A THIN OPAQUE HEAT-TRANSPARENTIZABLE SURFACE COATING COMPRISING A MIXTURE OF: (A) ONE HUNDRED PARTS BY WEIGHT OF PARTICLES OF TRANSPARENT WAXY MATERIAL FUSIBLE AT ABOUT 60-150* C.; (B) ABOUT 10-100 PARTS BY WEIGHT OF TRANSPARENT INFUSIBLE SILICEOUS PARTICLES LESS THAN ABOUT FOUR MILS IN DIAMETER; AND (C) SUFFICIENT TRANSPARENT FLEXIBLE ORGNAIC FILM-FORMING BINDER, WITHIN THE RANGE OF ABOUT ONE TO ABOUT SIX PARTS BY WEIGHT, TO PROVIDE GOOD RESISTANCE TO DUSTING AND RUB-OFF OF THE COATING WITHOUT CAUSING FLAKIUNG THEREOF; THE WAX, SILICEOUS PARTICLES, AND BINDER EACH HAVING SUBSTANTIALLY THE SAME REFRACTIVE INDEX, AND SAID BINDER BEING INFUSIBLE AT THE FUSION TEMPERATURE OF SAID WAX. 